The present invention relates to an optical disk and an optical disk drive apparatus. More specifically, the invention relates to an optical disk for recording data both onto the recording tracks in depressed portions formed by guide grooves and onto the recording tracks in protruding portions between the guide grooves, and an optical disk drive apparatus which uses the optical disk according to the present invention.
In recent years, in order to enhance a recording density of a large-capacity rewritable optical disk, a data recording method of recording data both onto guide grooves and onto lands therebetween has been studied. This method is generally referred to as a land-groove recording method. When this recording method is used, a higher recording density can be obtained. This is because the track pitch can be reduced by half compared to the case where only groove tracks are used for data recording.
Now, a conventional optical disk drive apparatus which uses the land-groove recording method is described. FIG. 9 is a block diagram showing a structure of an optical disk drive apparatus which is described in Japanese Unexamined Patent Publication 6-176404. Referring to FIG. 9, the optical disk drive apparatus is shown schematically for use with an optical disk 100. The optical disk drive apparatus includes a semiconductor laser 101 for emitting a laser beam. A collimator lens 102 converts the laser beam from the semiconductor laser 101 into a parallel beam. A half mirror 103 receives the beam and directs it toward an objective lens 104, which focuses the beam onto the optical disk 100. A photodetector 105 receives the reflected beam from the optical disk 100. The photodetector 105 includes two light-receiving parts divided by a boundary line parallel to the tracks of the optical disk 100 so as to obtain a tracking error signal.
The optical disk drive apparatus further includes an actuator 106 for driving the objective Lens 104, an optical head 107 enclosed by a dotted line and mounted on a head base, and a differential amplifier 108 for receiving a detection signal from the photodetector 105. A tracking polarity reversal circuit 109 receives the tracking error signal from the differential amplifier 108 and does or does not reverse the polarity of the tracking error signal, in response to a control signal T1 from a system controller 121. When the tracking error signal is supplied from the differential amplifier 108 to the tracking controller 110 without having its polarity reversed, the beam spot is pulled into a groove track. The tracking controller 110 receives an output signal from the tracking polarity reversal circuit 109 and a control signal T2 from the system controller 121 and supplies tracking control signals to a driving circuit 120 and a traverse motor controller 116.
A summing amplifier 111 receives detection signals from the photodetector 105 and supplies the sum of the signals. A waveform shaping circuit 112 receives a high-frequency component of the sum of the signals from the summing amplifier 111 and supplies digital signals to a reproduced signal processor 113 and an address reproduction circuit 114 respectively. The reproduced signal processor 113 supplies reproduced data to an output terminal. The address reproduction circuit 114 receives the digital signal from the waveform shaping circuit 112 and supplies an address signal to an address calculator 115. The address calculator 115 receives the address signal from the address reproduction circuit 114 and the control signal T1 from the system controller 121 and supplies the correct address signal to the system controller 121. The traverse motor controller 116 provides a driving current to a traverse motor 117 in response to a control signal T3 from the system controller 121. The traverse motor 117 moves the optical head 107 in the radial direction of the optical disk 100. A recording signal processor 118 receives recording data and supplies a recording signal to a laser diode (LD) driving circuit 119. The LD driving circuit 119 receives a control signal T4 from the system controller 121 and the recording signal from the recording signal processor 118 and supplies a driving current to the semiconductor laser 101. The driving circuit 120 supplies a driving current to the actuator 106. The system controller 121 supplies the control signal T1 to the address calculator 115 and the tracking polarity reversal circuit 109, the control signal T2 to the tracking controller 110, the control signal T3 to the traverse motor controller 116, and the control signal T4 to the recording signal processor 118 and the LD driving circuit 119.
The operation of the conventional optical disk drive apparatus having the above-mentioned structure is described with reference to FIG. 9. The laser beam emitted from the semiconductor laser 101 is made to be parallel by the collimator lens 102, passed through the half mirror 103 which is used as a beam splitter, and focused onto the optical disk 100 by the objective lens 104. The beam reflected from the optical disk 100 contains data on data recording tracks. The reflected beam is passed through the objective lens 104 and directed to the photodetector 105 by the half mirror 103. The photodetector 105 detects the strength and distribution of light in the incoming beam, converts it to electrical signals, and supplies them to the differential amplifier 108 and the summing amplifier 111.
The differential amplifier 108 applies a current-to-voltage conversion to the input currents, and in response to a potential difference between the input terminals thereof, produces a push-pull signal representing the difference between the two input signals. In response to the control signal T1 from the system controller 121, the tracking polarity reversal circuit 109 determines whether a track being accessed by the optical head is a land track or a groove track and reverses a tracking polarity only when the track being accessed by the optical head is a land track, for example. The tracking controller 110 supplies a tracking control signal to the driving circuit 120 according to the level of the tracking error signal received. In response to the tracking control signal, the driving circuit 120 supplies a driving current to the actuator 106 and controls the position of the objective lens 104 perpendicularly to the direction of the data recording tracks. The beam spot thereby scans the data recording tracks accurately.
The summing amplifier 111 receives output currents from the photodetector 105, applies a current-to-voltage conversion to them, and supplies the sum of the input signals to the waveform shaping circuit 112. The waveform shaping circuit 112 binarizes a data signal and an address signal in analog waveform in accordance with a predetermined threshold value and supplies the digital data signal and the digital address signal to the reproduced signal processor 113 and the address reproduction circuit 114, respectively. The reproduced signal processor 113 demodulates the input digital data signal, applies an error correction to the demodulated digital data, and supplies resultant data as reproduced data.
The address reproduction circuit 114 demodulates the input digital address signal and supplies disk position data to the address calculator 115. The address calculator 115 calculates the address of a sector being accessed by the optical head based on the address read from the optical disk 100 and the control signal T1 from the system controller 121 indicating whether a track being accessed is a land track or a groove track. The manner of address calculation will be described later. Based on the address signal, the system controller 121 determines whether the light beam is scanning a desired sector.
In response to the control signal T3 from the system controller 121, the traverse motor controller 116 supplies a driving current to the traverse motor 117 so as to move the optical head 107 to a target track. At the same time, the tracking controller 110 temporarily stops a tracking servo, in response to the control signal T2 from the system controller 121.
During normal data reproduction, the traverse motor 117 is driven in response to the tracking error signal from the tracking controller 110 so as to move the optical head 108 gradually in the radial direction of the disk with the progress of data reproduction.
The recording signal processor 118 adds error correction codes to the recording data which have been supplied at the time of data recording, modulates the recording data, and supplies an encoded and modulated recording signal to the LD driving circuit 119. When the system controller 121 has set the mode of the LD driving circuit 119 to the data recording mode by means of the control signal T4 supplied therefrom, the LD driving circuit 119 modulates a driving current to be applied to the semiconductor laser 101 based on the input encoded and modulated recording signal. The intensity of a beam spot formed on the optical disk 100 is thereby changed according to the recording signal, and recording marks are formed on the optical disk.
During data reproduction, the mode of the LD driving circuit 119 is set to the data reproducing mode by means of the control signal T4, and the LD driving circuit 119 controls the driving current in such a manner that the semiconductor laser 101 emits a laser beam of a constant intensity. The recording marks and prepits on the data recording tracks of the optical disk 100 can be thereby detected.
A single spiral land/groove format is now described. A conventional optical disk, in which the land-groove recording method is used, has a continuous spiral of groove tracks, and land tracks are also in a separate continuous spiral form.
FIG. 10 is a diagram showing another conventional optical disk having a format in which land tracks L and groove tracks G are connected alternately so as to form a single spiral of data recording tracks. An optical disk having such a format, hereinafter referred to as a single spiral land/groove format (SS-L/G format), is disclosed in Japanese Unexamined Patent Publication 4-38633.
When a tracking servo is applied to an SS-L/G format optical disk, it is necessary that connecting points CP which connect a groove track C and a land track L be detected correctly, and a tracking servo polarity be switched to control a tracking servo system so as to track on a groove track or on a land track.
A description is now directed to the methods of inserting identification signal prepits on an optical disk for producing identification signals for which the land-groove recording is performed and which is used by an optical disk drive apparatus. The three methods of inserting identification signal prepits, as shown in FIG. 11A through FIG. 11C, are known. In these figures, HF denotes header parts and DRF denotes data parts.
In the method shown in FIG. 11A, land track sectors and groove track sectors have their own sector addresses, respectively. If the width of prepits representing an identification signal were set to be identical to the width of a groove, the prepits between the adjacent tracks would be connected to each other, and the identification signal could not be detected correctly. For this reason, the width of the prepits is set to be smaller than that of a groove, and normally is set to be around a half of the width of a groove. For inserting prepits having a width different from that of a groove continuously during the mastering process of mother stamper in disk fabrication, the diameter of a laser beam for forming the prepits must be different from that for forming the groove. This means two separate laser beams must be used for forming grooves and prepits. If the laser beams are not aligned in-line during the formation of grooves and prepits, a tracking offset will occur between the reproduction of identification signals from the prepits and the recording/reproduction of data recording signals. The quality of the reproduced data will therefore deteriorate. More specifically, due to the deviation of tracking, the error rate of the reproduced data will increase, leading to lower reliability of the reproduced data. For this reason, highly accurate positioning of the two laser beams is required during the formation of prepits and grooves, which will be a factor raising the cost of disk fabrication.
In view of the above-mentioned problem, and in terms of the accuracy and the cost of the fabrication of an optical disk, it is preferable that identification signal prepits should be formed in accordance with the method shown in FIG. 11B or FIG. 11C, where grooves and prepits can be formed by means of a single laser beam. FIG. 11B and FIG. 11C respectively show different methods of inserting prepits having substantially the same width as the width of the grooves.
FIG. 11B shows a conventional optical disk described in Japanese Unexamined Patent Publication 6-176404. The optical disk in FIG. 11B uses a method of inserting prepits which is also referred to as a land/groove common address method. In this method, identification signal prepits are disposed around the center of a pair of adjacent groove and land tracks, and the same identification signal prepits are shared by the sectors in the groove and land tracks.
FIG. 11C shows another L/G individual address method. In this method, individual addresses are provided for land and groove track sectors, respectively. The positions of the identification signal prepits for the land and groove track sectors adjacent to each other are shifted relative to each other in a direction parallel to the tracks such that they do not overlap each other in the radial direction. Japanese Unexamined Patent Publication 7-110944 discloses an example of this method.
When the above-mentioned conventional method of providing sector addresses is applied to an SS-L/G format optical disk illustrated in FIG. 10, the following problems will occur. Let us assume, for example, that, in the aforementioned method described in Japanese Unexamined Patent Publication 6-176404 and shown in FIG. 11B, the position of prepits is shifted by a predetermined distance, such as half a track pitch (a full track pitch being defined as the distance between the centers of the land and groove tracks adjacent to each other), from the center of a groove track. In the SS-L/G format optical disk, land and groove tracks are connected in every revolution. FIG. 12 shows arrangements of land and groove tracks immediately before and after a connecting point CP. Identification signal prepits for a groove track sector are formed in the leading end thereof, and are shifted by half a track pitch, in the radially outward direction OP from the center of the groove track. These prepits are at a position half a track pitch radially inward (IP) from the center of a land track sector adjacent to and radially outside of the above-mentioned groove track. When a beam spot scans along a groove track, a radially outer half of the reflected beam is modulated by the preformatted identification signal, and the identification signal for the groove track sector is thus detected. When the beam spot scans along a land track, a radially inward half of the reflected beam is modulated by the preformatted identification signal, and the identification signal for the land track sector is thus detected. This means that the same identification signal is produced for the groove track sector and for the land track sector which is adjacent to and outside of the above-mentioned groove track sector. The system controller 121 knows whether the beam spot is scanning a groove track sector or a land track sector, that is, it recognizes the tracking polarity. The track sector address can therefore be identified by the address calculator 115, according to the address data obtained from the address signal from the address reproduction circuit 114 and the control signal T2 from the system controller 121.
As shown in FIG. 12, the address of a groove track sector immediately after a connecting point CP is set to # n. Now, let us assume that the number of sectors in one recording track is N. Then, the address of the groove track sector immediately before the connecting point CP after one revolution of the track will be # (n+N-1). This sector is connected to a land track sector at the connecting point. This land track sector immediately after the connecting point adjacent to and outside of the above-mentioned groove track sector has the address which is common to the groove track sector. Thus, the address of the sector becomes # n again. Similarly, the address of the land track sector immediately before the connecting point after a further revolution of the track will be # (n+N-1). This land track sector is connected to the groove track sector having the sector address # (n+N). As described above, the N groove track sectors and the N land track sectors alternate to form a continuous spiral of data recording tracks. FIG. 13 shows a change in a sector address in this data recording spiral.
In a conventional optical disk such as a compact disc or a magneto-optical disk, either a land or a groove is used as a data recording track. Generally, the data recording tracks on the optical disk form a data recording spiral, and sequential addresses are assigned to the sectors arranged in the data recording spiral. Thus, since the relationship between a sector and an address number thereof is very simple, the optical head can easily access a target sector. On the contrary, if the conventional addressing scheme is applied to an SS-L/G format optical disk, the sector address value will not change monotonically with the sector position in the data recording spiral, as shown in FIG. 13. The physical position of a sector in the data recording track spiral cannot be identified until the readout address of the sector is converted to the address value representing the arrangement sequence of the sector in the data recording spiral in consideration of the tracking polarity of the sector recognized by the optical disk drive apparatus. Whenever the optical head of the optical disk drive apparatus is going to access a specific sector in the optical disk, the above-mentioned address calculation is required. Especially, whenever the optical head makes a series of non-sequential access to sectors, such complex address calculation is required. This imposes a considerably heavy burden on the optical disk drive apparatus.
The above-mentioned problem is further manifested in the case of a format used in a high-density optical disk. In a ZCAV (Zoned Constant Angular Velocity) format or a ZCLV (Zoned Constant Linear Velocity) format, in which the recording area of an optical disk is divided into a plurality of annular zones and a more outward zone of the disk has a greater number of data recording sectors per data recording track, the number of sectors per track indicated by N as shown in FIG. 12 or FIG. 13 changes with the radial position of a track in the optical disk. For this reason, the above-mentioned address calculation for determining the physical position of a sector in a data recording spiral based on both the address of the sector and the tracking polarity will become further complex.
In the case of the L/G independent address method as shown in FIG. 11C, nothing is disclosed in Japanese Unexamined Patent Publication 7-110944 about how the addresses are assigned to the sectors. A method can however be conceived in which separate sequences of addresses are assigned to the sectors in the groove track spiral and sectors in the land track spiral. The relationship between the position of a sector in data recording spirals and the address of the sector is the same as that illustrated in FIG. 13, like the case where identification signal prepits are formed in accordance with the land/groove common address method illustrated in FIG. 11B.
In this case, however, it is not necessary to discriminate between a land track sector and a groove track sector, based on the tracking polarity recognized by the optical disk drive apparatus, unlike the case where the land/groove common address method is used. This is because discrimination between a land track sector and a groove track sector can be made according to a reproduced identification signal. However, the address calculation for determining the position of a sector in a data recording spiral is still complex.
Now, a description will be directed to the problems of the servo system. In an SS-L/G format optical disk, both lands and grooves are used for data recording. Thus, a higher track density can be obtained. However, because of this higher track density, when a tracking offset is increased, the quality of a reproduced signal is lowered because of crosstalk from an adjacent track and the error rate increases due to an increase in jitter. The problem of crosserase of data on an adjacent track may also occur during data recording. A tracking error signal which will cause a tracking offset is generated due to combined effects of the optical head system, the arrangement of tracks in an optical disk, and the servo system. Accordingly, the detected error signal level is different between a land track and a groove track, in general. In order to eliminate crosstalk and crosserase, different offset compensations are required between a land track and a groove track. In a conventional optical disk having a groove track spiral and a land track spiral, a track offset compensation can be made separately for each of the data recording track spirals during the continuous tracking operation gradually, taking a certain time period until an optimum amount of tracking compensation is found. After the adjustment, the amount of compensation can be retained. Thus, a track offset compensation can be made easily. On the other hand, in the case of an SS-L/G format optical disk, a tracking polarity is reversed every revolution. The tracking offset compensation should therefore be made quickly.
In connection with the method of inserting identification signals in FIGS. 11A, 11B, and 11C, adequate consideration has not been given to the above-mentioned track offset compensation. In the case of the land/groove common address method illustrated in FIG. 11B, for example, throughout the period in which an identification signal is scanned, the identification signal prepits are only on one side of the beam spot, so that the tracking offset keeps increasing. On the other hand, in the case of the L/G independent address method illustrated in FIG. 11C, detection of a tracking offset is difficult, like the case of the land/groove common address method illustrated in FIG. 11B.
As has been described, when any of the above-mentioned three methods of inserting identification signal prepits is applied to the SS-L/G format optical disk, the sector address calculation will become complex. Further, in the SS-L/G format optical disk, tracking offset compensation should be made quickly, but detection of a tracking offset is difficult. Still further, in the SS-L/G format optical disk, a connecting point between land tracks and groove tracks should be detected easily.